Imaging by in situ Scanning Tunnelling Microscopy and its Nanotechnological Perspectives

1 Department of Chemistry, Technical University of Denmark2 Department of Chemistry, Technical University of Denmark

Abstract:

The development of in situ Scanning Tunneling Microscopy (in situ STM) and the implementation to scientific investigations is documented. The term ‘in situ’ that is added to the STM refers to an advanced development of the microscope, which encompasses tip coating and bipotentiostatic control of the tip and working electrode. In collaboration with Danish Micro Engineering A/S, the instrument was constructed and tested in laboratory environments. The system was successfully developed, as to meet international-market requirements. Within the frame of the work, procedures of tip coating and bipotentiostat construction were evaluated. After the fulfilment of the instrument manufacturing process followed application of the system to scientific investigations. The generation of an image by in situ STM is founded on the principle of electron tunneling but the application of the instrument to aqueous conditions introduces an influence of electrochemical currents to the image interpretation. The corresponding technique where the image is exclusively generated by electrochemical currents is denoted as Scanning Electrochemical Microscopy (SECM). The combined current contributions are considered in the interpretation of the imaging procedure. Other methods of in situ Scanning Probe Microscopy (in situ SPM), such as in situ Scanning Force Microscopy (in situ AFM) are considered for the sake of comparison and they are applied to imaging of non-conducting systems. Major results include demonstration of atomic resolution at Au(111) in electrolyte, imaging of bulk-metal electrocrystallisation, imaging of pulse plating and imaging of single-molecule metalloproteins in the adsorbed state. Methods of covalent immobilisation of proteins, which enables imaging by in situ STM were developed. The combination of simultaneous imaging and electrochemical manipulation offers unprecedented possibilities of device construction at the nanometer level. The present work is therefore intended as a promotion of in situ STM as a tool of nanotechnology that allows device fabrication of sub-nanometer tolerances. Novel applications and disclosures are included in the presentation with emphasis on thiol self-assembled monolayers (SAM’s), on electrochemical-surface manipulations and on imaging of proteins. Evidence of the validity of successful imaging of adsorbed metalloproteins is presented and perspectives of nano-biotechnology are evaluated. It is thus documented that in situ STM constitutes an indispensable tool of nanotechnology. Keywords are imaging and control. The manufacture of nanotechnological devices is exemplified by construction of a ‘nanotypewriter’ that exploits a novel feature of electrochemistry. The nanotypewriter is patented in Denmark and U.S.A.